Carryover of polar bases in plasma
Posted: Thu May 21, 2009 10:52 am
Wondering if anybody has ideas about a carryover problem I have here 
I'm injecting a mixture of moderately polar (log P -1 to -4) and weakly basic (pKa 7-9) compounds (Mwt. ~300) onto a polymeric TFC column in diluted plasma samples. Column carryover seems to be a consistent problem in the range 1-2 % but reduces slowly when I make repeated blank injections. The loading mobile phase i'm using is 10mM Ammonium Carbonate (pH 9).
After trying several washing steps such as acetic acid, trifluroacetic acid, ammonium formate, acetonitrile/acetone, 1% ammonia soln I am still having the same problems. Replacing the column eliminates carryover temporarily and performing blank injections through the autosampler but without a column removes the carryover.
Appreciate if anybody has any ideas? Due to the compound polarity I'm presuming ionic interactions are more the problem. How can these be eliminated?
Thanks
Paul
I'm injecting a mixture of moderately polar (log P -1 to -4) and weakly basic (pKa 7-9) compounds (Mwt. ~300) onto a polymeric TFC column in diluted plasma samples. Column carryover seems to be a consistent problem in the range 1-2 % but reduces slowly when I make repeated blank injections. The loading mobile phase i'm using is 10mM Ammonium Carbonate (pH 9).
After trying several washing steps such as acetic acid, trifluroacetic acid, ammonium formate, acetonitrile/acetone, 1% ammonia soln I am still having the same problems. Replacing the column eliminates carryover temporarily and performing blank injections through the autosampler but without a column removes the carryover.
Appreciate if anybody has any ideas? Due to the compound polarity I'm presuming ionic interactions are more the problem. How can these be eliminated?
Thanks
Paul